1. Field of the Invention
The present invention relates generally to a digital signal delivery systems, and in particular, to design and implementation for Low Density Parity Check (LDPC) codes for multiple-input, multiple-output channels within a digital signal delivery system.
2. Description of the Related Art
Radio Frequency (RF) transmission of information has become commonplace. Typically, a single transmit antenna sends a signal which can be received by one or more receive antennas. Examples of such systems include satellite broadcasts, such as satellite television broadcasting, radio, and cellular telephone systems.
Because of the ease of use of such systems, larger and larger demands for higher speed data transfer through such systems have taken place. Wireless internet access, which requires the transfer of large amounts of data for pictures, audio, and other data requires a large throughput via a single transmit antenna system. Many of these systems are now reaching their data throughput limits, making it difficult to provide wireless data transfer in areas that such services are desired.
There is a current movement to have Multiple Input Multiple Output (MIMO) systems that employ multiple transmit antennas and multiple receive antennas to increase the data throughput. Examples of MIMO systems are wireless Local Area Networks (LANs), Bluetooth networks, and high-speed wireless (Wi-Fi) networks. MIMO systems use multiple signal paths, which in standard systems would cause multipath errors and interference, to transmit additional data from one place to another. Algorithms for properly transmitting and subsequently recombining the MIMO transmitted data at the receiver must be conceived and transmitted along with the MIMO data for such systems to properly function.
MIMO systems theoretically double the spectral efficiency compared with that of single transmit antenna systems. Just as with single transmit antenna systems, the data frames in a MIMO system are coded in such a manner that they can interfere with each other, and MIMO receivers cannot tell which packets of data goes first, or whether the data within a given frame is corrupted by constructive or destructive interference. Such interference is called “co-channel” interference, where one channel of data interferes with the reception and demodulation of another channel of data. In practical applications, the co-channel interference may also stem from transmission of other system operators or other spot transmission beams in a MIMO system. As MIMO systems transmit more data, the interference between data packets will increase, and, as such, the quality of the signal reception will be poorer.
To ensure that transmission systems can properly decode transmitted data, error correction codes, specifically, Forward Error Correction (FEC) codes are used. However, in MIMO systems, FEC codes cannot be chosen randomly because of the potential interference of these codes with each other.
Traditionally, the negative effects of such interference have been minimized by redesigning the frequency assignments assigned to the various transmitters and receivers. However, since the frequencies are fixed by standard, frequency reassignment or frequency reuse will not alleviate the problem beyond a certain point.
It can be seen, then, that there is a need in the art to minimize the interference in a broadcasting system. It can also be seen that there is a need in the art for proper selection of FEC codes in a MIMO system.